1. Field of the Invention
The present invention relates to a heat exchange belt conveying apparatus, in particular for thin sheet products and the like, of the type comprising a support structure; one guide roller rotatably mounted according to a horizontal axis on the support structure; a second guide roller rotatably mounted according to a horizontal axis on the support stucture in a position spaced apart from the first guide roller; a continuous belt made of a material having a high heat conductivity and extending so as to form an endless strap around the guide rollers thereby creating a first going stretch extending over the guide rollers and designed to transport a sheet-like product which is laid thereon adjacent the first guide roller, as well as a return stretch extending underneath th first going stretch and said rollers; a motor operating on at least one of the guide rollers to drive them in rotation so that the product is carried towards the second guide roller due to the displacement of said belt; and first thermoregulation means acting on the lower surface of the first belt stretch in order to carry out, through the latter, a heat exchange with the product carried by the belt.
More particularly, the apparatus in question can be, for example, installed at the outlet of an extruder for carrying out the cooling of a proudce extruded in the form of a thin sheet. The apparatus of the invention can however be used as a heating means as well, for example for carrying out the drying or polishing of particular products.
For the sake of clarity, in the following, particular reference will be made to the use of the apparatus as a cooler, although the possibilities of use of the same are not limited thereby.
2. Prior Art
It is known that there are belt conveying apparatuses which not only carry out the transport of the product laid thereon, but are also capable of performing an efficient heat exchange action with the product itself.
In their simplest embodiments, these apparatuses are essentially comprised of two guide rollers around which a steel belt extends so as to form an endless strap which is driven by effect of the rotation communicated to the guide rollers upon command of a motor. The belt defines a going stretch extending above the guide rollers and transporting the product in progress of working which has been laid thereon, and a return stretch extending underneath the going stretch.
Acting in the region of the going stretch is thermoregulation means designed to cause the withdrawal or delivery of heat respectively from and to the product carried thereon. If the aspparatus is used as a cooler said thermoregulation means may for example consist of a number of nozzles sprayig cold water onto the lower surface of the going stretch of the belt, so as to cause the cooling of the product by conduction through the belt itself. In order to achieve a more efficient cooling of the product it is also possible to blow cold air thereon so that a cooling action by convention can be added to the above cooling action.
One of the most important problems connected with the use of apparatuses of this type resides in the length of the going stretch of the belt which must be sufficient to achieve the desired heat exchange with the product in progress of working. As said length increases in proportion to the aimed productivity and to the amount of heat to be exchanged, the apparatus must necessarily be very bulky and therefore its installation becomes problematical.
In order to eliminate this drawback as far as possible, the apparatuses of the known art have been provided with a second steel belt wound around respective rollers and having a portion of its length extending above the going stretch of the first belt; said second belt moves at the same speed as the first belt.
The product being worked is therefore enclosed between two belts and water is delivered to each of them in order to achieve a cooling by conduction on both surfaces of said product.
This solution gives rise to a more efficient heat exchange with the product being worked and therefore allows the length of the going stretch of the belt to be reduced with respect to the previously described solutions, the required productivity and the amount of heat to be exchanged being equal.
But, on the other hand, apparatuses with two belts have a very complicated structure and, as a result, high production costs.
In addition, it is always rather difficult to achieve an optimum contact, and therefore an optimum heat exchange, between the upper belt and the product, because said contact is exclusively the result of the catenary which tends to be formed along the lower portion of the belt.